I am learning Java Swing for 2 days and trying to do some simple codes for better learning.

I have three(can be more) nested elllipse. I want to fill the gaps between the ellipses with different colors. However, have little coordinate problem. That piece of code can properly draws 3 circles (or whatever number you want). I just want to fill the gaps between those nested circles with different colors. How to use fill method and how to give it correct coordinate parameters to do that job?
Thanks in advance.